The present invention relates to light emitting devices and a method for fabricating the same.
In general, a light emitting device is fabricated by growing gallium nitride (GaN) crystals into a thin film. The best choice of growing the GaN crystals is a GaN substrate.
However, the GaN substrate is very expensive due to difficulty in growing GaN crystals, and the like.
Therefore, most of GaN-based light emitting devices are grown on heterogeneous substrates. The heterogeneous substrates include sapphire (A1203), silicone carbide (SiC), gallium arsenide (GaAs) and the like. Recently, a sapphire substrate among the heterogeneous substrates has been widely used.
FIGS. 1a to 1e are sectional views illustrating a conventional method for fabricating GaN-based light emitting devices. As shown in FIG. 1a, a plurality of light emitting structures (10) are formed on a sapphire substrate (20), each structure being spaced apart from one another.
Here, each of the plurality of light emitting structures (10) includes an active layer for generating light.
In addition, a P-electrode is deposited on each of the plurality of light emitting structures such that the P-electrode is in ohmic contact therewith, thereby stably supplying an external current to the light emitting structure.
Thereafter, a metallic film (30) is formed to wrap the plurality of light emitting structures (10) by means of plating or the like (FIG. 1b).
At this time, since the metallic film (30) holds the light emitting structures (10), the sapphire substrate (20) can be easily removed in a subsequent process.
Then, the sapphire substrate (20) is separated from each bottom of the light emitting structures (10) (FIG. 1c).
The sapphire substrate (20) may be removed using a laser lift off process.
Here, the laser lift off process is a process of separating and removing the sapphire substrate from the plurality of light emitting structures (10) wrapped by the metallic film (30), by irradiating a laser beam from below the sapphire substrate (20).
At this time, energy generated during the metallic film forming process and the laser lift off process is transferred directly to the metallic film, resulting in generation of stress in the metallic film
Thus, defects such as cracking or bending of the metallic film occur. These defects lead to defective devices, thereby lowering a production yield of devices.
As shown in FIG. 1d, after the sapphire substrate is separated, a scribing process is performed to form a cutting groove (40) on the metallic film between adjacent light emitting structures (10) each structure spaced apart from each other.
At this time, the rigidity of metal itself may cause a crack (41) under the cutting groove (40). Further, the crack (41) may propagate to the light emitting structures, resulting in degradation of the quality of light emitting devices.
Finally, as shown in FIG. 1e, an expanding and breaking process is carried out, wherein a physical force is exerted on the adjacent light emitting structures wrapped by the metallic film (30) so as to individually divide the light emitting structures.
In the conventional fabrication process, the groove is formed on the metallic film to divide the light emitting structures and then used to perform the breaking process. However, since a lower portion of the metallic film may not be cut occasionally, there is a problem in that all the light emitting structures cannot be completely divided.
Particularly, if the metallic film is formed of a material with high ductility such as copper, the metallic film is easily stretched, causing difficulty in dividing the light emitting structures.
In addition, as described above, there is a high possibility that the crack (41) of the metallic film generated during the scribing process may propagate to the light emitting structures when the light emitting devices are divided.
Of course, there is a method for maximally reducing the propagation of the crack to the light emitting structures by increasing spacing between the light emitting structures. In this case, however, the number of devices to be integrated on a single wafer is decreased, resulting in inevitable reduction of a yield. This method is not a proper solution since there is a problem in that the existing scribing process should be improved.